The present invention relates generally to proximity detection systems at work sites, and in particular to an interactive magnetic marker field and proximity warning system. Many methods have been devised to protect people from being struck, pinched, crushed or otherwise harmed by vehicles and mobile equipment. Such vehicles and mobile equipment may be used for above and below ground operations. Examples of the equipment include: road construction equipment such as trucks, road graders, rollers and pavers; surface mining equipment, such as for use with gravel and sand operations, front end loaders, trucks, dozers, conveyors and other items; underground mining equipment such as continuous miners, shuttle cars, conveyors, crushers, load-haul-dump vehicles, man-trips, tractors, and other items. The equipment also includes fork lifts, cranes, and trucks used at warehouses and shipping ports.
Hundreds of people are killed each year in the US by such equipment. Unfortunately, the systems that have been devised to protect people and property in these industrial operations, such as proximity protection and collision avoidance systems have usually not been very effective. A new proximity protection system, sometimes referred to as a collision avoidance system, was developed and successfully demonstrated for use on continuous miners, as disclosed in U.S. Patent Application Publication 2006/0087443, which is incorporated in its entirety by reference herein. An objective of the '443 publication was to prevent the crushing or pinning of personnel who are remotely controlling a continuous miner, and to protect other personnel assisting in use of the continuous miners. The '443 publication also envisioned to provide protection to personnel from other types of mobile equipment and machines. The system of the '443 publication employs a magnetic marker field and an active architecture that incorporates two-way communication between the person being protected and the machine from which the person is being protected. Warnings are given to workers that are dangerously close to the miner. Warnings are also provided to the operator of the machine. Provisions are made to immobilize the equipment until personnel were able to reach a safe position.
The '443 publication, however, did not provide an architecture that was fully adequate for environments where there are many personnel working in close proximity to multiple equipment in the same workspace. For example, it is essential that a signal or response by the system be directed only to the machine, and/or the machine's operator, that is threatening a worker's safety. Otherwise, a signal or response from the system will result in unnecessary signals or responses to other, unaffected machines and/or workers. Such unnecessary signals and responses result in unwanted false alarms. False alarms and nuisance alarms have been known for years to be a major reason why many proximity protection systems and collision avoidance systems have failed when in real operational environments.
False alarms or nuisance alarms have traditionally been the primary reason for failure of deployed proximity systems. In real industrial environments, proximity systems have experienced many forms of errors as well as problems related to the shape of the protection zones. Such errors and problems are discussed in the NIOSH Report RI 9672, titled “Recommendations for Evaluating & Implementing Proximity Warning Systems on Surface Mining Equipment,” of the Department of Health and Human Services.
An example of what happens when alarms are sounded without there being a real danger can be explained with respect to standard backup alarms required by law for most industrial vehicles. When the vehicle or machine begins to back up, a horn is typically sounded. In a work environment where there are many vehicles or machines, there typically are many horns sounding very frequently. Such horns are soon ignored by the workers. This is because it is not realistic for each worker to stop to consider every horn sounding within their work area. Even when there is only one vehicle, if that vehicle is frequently backing up and the workers frequently hear the horn sound while knowing that their safety is not being threatened, the workers will soon begin to ignore the warning horn or alarm. Then, when their safety actually is threatened, the horn provides no protection because the workers would disregard the horn, believing it to be just another false alarm. Thus, the worker should be warned only when there is a threat to them.
Previous proximity and collision avoidance systems have not been effective in reliably warning only of real threats to safety, while also avoiding giving alarms when there is no real danger to the worker. Analysis of prior art collision warning systems are discussed in a publication from SAE International, titled “Development and Testing of a Tag-based Backup Warning System for Construction Equipment,” No. 2007-01-4233. The shortcomings have been found to exist for work sites where only one machine and a worker are operating. The shortcomings are magnified in complex work areas, areas involving many elements. Another proximity protection concept has been under development for use at work sites, such as road construction sites, surface mining, loading docks, etc., where multiple machines and vehicles routinely work in close conjunction with each other, and where many workers work within the area around the machines. Based upon tests, a need has been identified for restricting the defined hazard zones such that workers can approach a vehicle at the side or front without producing alarms.
Another challenge for proximity detection systems is that the operators of vehicles and equipment may frequently dismount and/or leave the equipment that they are operating. Existing proximity detection systems do not distinguish between situations when the operator is riding in his vehicle or machine—situations where the system should not produce a warning or take an action to immobilize the vehicle—and situations where the operator dismounts and moves around the vehicle, when full protection for the operator is needed.
Given the rapid growth of radio frequency identification (RFID) technologies worldwide, consideration has been given to using RFID technologies and schemes for proximity protection. A major drawback with using RFID technologies is that this approach depends upon radio frequency (RF) transmissions at high frequencies in the electromagnetic spectrum. Since the maximum range of some types of RF systems is almost unlimited, up to miles, if needed, it might seem to be a good candidate, for that reason, for collision avoidance systems, particularly when the vehicles are traveling at higher speeds. Also, the higher frequencies can provide much greater bandwidth, which allows implementation of many special functional features. In complex work environments, however, there are many metallic materials and surfaces that reflect the RF signals, causing the RF signals to travel over multiple paths. If the RF receivers are used to measure the strength of RF signal, in order to determine the distance between the vehicle and the person to be protected, these reflections over multiple paths can cause errors in the measurements. Radar systems are prone to identify most any objects within the defined hazard zones, even though the objects are no threat to safety. GPS signals have also been found to be affected by reflections of nearby equipment, causing a mis-calculation of the distance between the receivers and the vehicles. As a consequence, a reliable marker field (for a proximity detection zone, for example) can not be maintained with high frequency RF systems. In addition, RF signals do not easily pass through earth formations; as such, personnel may be shielded from the proximity detection system until it is too late to take evasive actions. Even medium frequency magnetic fields have been found to propagate on cables and pipes, making medium frequency magnetic fields less reliable than desired.
In contrast to RF fields, magnetic fields, oscillating at low frequencies, are known to be stable and can be effectively used to mark off silent zones or danger zones. Such technologies are discussed in U.S. Pat. Nos. 6,810,353 and 5,939,986 to Schiffbauer, which are incorporated by reference herein. Although the maximum practical range of such low frequency magnetic fields may be less than 50 feet in most applications, that is more than is needed or desirable for most equipments. Typical haul trucks would probably be best served with a warning zone in the range of 20-30 feet and a danger zone in the range of 10-15 feet. In some applications, such as remotely controlled continuous miners, it is necessary for the operator to remain within a range of 10-25 feet much of the time in order to maintain good visual contact with the machine and the immediate surroundings. In underground mines, the magnetic fields pass through earth formations unimpeded so that a worker that is around a corner, not in line of sight, or otherwise obstructed, will still be visible to the marker field. These magnetic fields do not radiate from antennas but simply expand and contract around the element that produces them, and are well suited for marking boundaries between safe zones and unsafe zones. An attempt has been made to apply identification information (IDs) to magnetic fields as part of proximity protection or collision avoidance strategy. There are serious limitations to this approach, however, particularly where there are numerous elements (machines, workers, etc.) involved at a work site. At low frequencies bandwidth is limited, thus limiting the processes that would typically be employed. If two adjacent machines are transmitting their IDs at the same time, the low frequency fields may conflict, causing the amplitude of the composite field to vary, causing errors in the data set. With low frequency markers fields, the bandwidth available is not sufficient to allow rapidly re-sending data sets and use algorithms to remove the errors. There are numerous possible interactions between many elements, the circumstances of which may sometimes be ignored, but may also be critical to safety.
Conflicts between the fields produced by the multiple systems easily occur. Workers may find themselves within the magnetic fields of more than one machine and coordination of the system responses can be degraded and unreliable. For example, if a Personal Alarm Device, used to personally warn a worker of a safety threat, is in two hazard zones, of two machines, and one is a greater threat, the Personal Alarm Device must be able to determine which is the greatest threat and respond accordingly. At the same time, the operator of a machine needs to be given the appropriate alarm for that machine, not the alarm that is appropriate for the second machine. When there are three or four machines that are in the same area, working closely together, it is critical that the workers around each and the operator of each do not receive confusing indications. If the alarms are confusing, the proximity detection system will not be used. What is needed is a proximity system that can reliably accommodate an environment having multiple moving elements.
There is also a need for a way to transmit information from each worker to log events, such as safety-related event, that are experienced, to allow use of the system to track personnel during an emergency, for example. There is also a need to provide a means to collect data related to the location and safety of an individual worker. In addition, there is a need for workers to be able to provide interactive responses to equipment and/or operators.
Moreover, although low frequency fields are ideal for marking off protection zones or danger zones because they are very stable, this stability in field shape is a disadvantage in some cases. For example, there are situations where it is desirable for workers to be close to equipment at one location but not close at another location. An example is a truck that is backing up. A worker at the side of the truck is at a very low risk or possibly no risk at all; yet, a worker behind the truck may be at a very high risk. Magnetic fields that extend far enough behind the truck to provide the needed protection, however, will also produce a larger than desired field to the sides of the truck. There is also a need, therefore, to be able to shape a marker field to exclude areas where workers need to be positioned, and/or areas that present no safety risk, for example. Moreover, what is needed is a special system design and architecture for a reliable proximity warning or collision avoidance system that will avert the many hazards that exist in the many, diverse industrial work environments.